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Prostate Motion and Dose Distribution in Prostate Patients Without Rectal Balloon During a Course of Proton Therapy

R Regmi1*, D Maes2 , J Saini3 , T Wong4 , J Liao5 , R Rengan6 , J Zeng7 , (1) ,Bothell, WA, (2) SCCA Proton Therapy Center, Seattle, WA, (3) SCCA Proton Therapy Center, Seattle, WA, (4) SCCA Proton Therapy Center, Seattle, WA, (5) University of Washington Medical Center, Seattle, WA, (6) University of Washington, Seattle, WA, (7) SCCA Proton Therapy Center, Seattle, WA


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Rectal balloons distends rectum wall reducing the total rectal volume receiving high dose, and also reduce prostate motion. However, the use of rectal balloons increases cost, causes discomfort, and adds treatment time. Objective of this study is to investigate the prostate motion, target coverage, and dose to OARs in prostate patients without the rectal balloon in proton therapy.

Methods: Seven prostate patients that were treated without rectal balloon were evaluated. Each of these patients had three implanted fiducial markers in the prostate for image guided proton therapy with a 2D KV orthogonal imaging system. Three quality assurance CT scans (QACTs) at different time interval were taken for each patient during the course of proton therapy. Dose distributions on QACTs were estimated and compared to original planning CT. The prostate motion was measured by evaluating relative shifts between bony anatomy and fiducial markers.

Results: In six out of the seven patients, PTV coverage in QACTs was within 5% as compared to planning CT. For one patient, PTV coverage decreased by 16.5% due to increase in patient weight and subsequent extra tissue in beam path leading to create adaptive plan. In most of the patients, change in rectum and bladder dose during the course of treatment was within 10% due to prostate motion, and variation in rectum and bladder fillings. The interfraction prostate motion was within the tolerance of treatment plan robustness of 1 cm.

Conclusion: In the absence of rectal balloon, interfraction prostate motion was within the tolerance of plan robustness and does not affect PTV coverage. Most of the dose constraints for rectum and bladder were met and didn’t trigger an adaptive plan.

Funding Support, Disclosures, and Conflict of Interest: None


Not Applicable / None Entered.


TH- External Beam- Particle therapy: Proton therapy - quality assurance

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